tee: optee: add registered buffers handling into RPC calls

With latest changes to OP-TEE we can use any buffers as a shared memory.
Thus, it is possible for supplicant to provide part of own memory
when OP-TEE asks to allocate a shared buffer.

This patch adds support for such feature into RPC handling code.
Now when OP-TEE asks supplicant to allocate shared buffer, supplicant
can use TEE_IOC_SHM_REGISTER to provide such buffer. RPC handler is
aware of this, so it will pass list of allocated pages to OP-TEE.

Signed-off-by: Volodymyr Babchuk <vlad.babchuk@gmail.com>
[jw: fix parenthesis alignment in free_pages_list()]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>